<?php

/**
 * Validate an email address.
 * Provide email address (raw input)
 * Returns true if the email address has the email 
 * address format and the domain exists.
 */
function validateEmail($email) {
	$isValid = true;
   	$atIndex = strrpos($email, "@");
   	if (is_bool($atIndex) && !$atIndex) {
    	$isValid = false;
   	} else {
      	$domain = substr($email, $atIndex+1);
      	$local = substr($email, 0, $atIndex);
      	$localLen = strlen($local);
      	$domainLen = strlen($domain);
      	if ($localLen < 1 || $localLen > 64) {
         	// local part length exceeded
         	$isValid = false;
      	} else if ($domainLen < 1 || $domainLen > 255) {
         	// domain part length exceeded
         	$isValid = false;
      	} else if ($local[0] == '.' || $local[$localLen-1] == '.') {
         	// local part starts or ends with '.'
         	$isValid = false;
      	} else if (preg_match('/\\.\\./', $local)) {
         	// local part has two consecutive dots
         	$isValid = false;
      	} else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
         	// character not valid in domain part
         	$isValid = false;
      	} else if (preg_match('/\\.\\./', $domain)) {
         	// domain part has two consecutive dots
         	$isValid = false;
      	} else if(!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/', 
      		str_replace("\\\\","",$local))) {
         	// character not valid in local part unless 
         	// local part is quoted
         	if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\","",$local))) {
            	$isValid = false;
         	}
      	}
      	
      	if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A"))) {
         	// domain not found in DNS
         	$isValid = false;
      	}
	}
   	return $isValid;
}